In a conventional mobile communication system, a radio network controller RNC is configured to determine a transmission rate of a dedicated channel while taking into consideration radio resources of a radio base station Node-B, the amount of uplink interference, a transmission power of a mobile station UE, a transmission processing performance of the mobile station UE, a transmission rate required by an upper application or the like; and then to notify the determined transmission rate of the dedicated channel to each of the mobile station UE and the radio base station Node-B through a layer 3 (Radio Resource Control Layer) massage.
Here, the radio network controller RNC is a device that exists at a higher level than the radio base station Node-B, and that controls the radio base station Node-B and the mobile station UE.
In general, data communications often cause burst traffic compared to voice communications or telecommunications. For this reason, it is desirable that the transmission rate of a channel used for data communications be changed rapidly.
However, as shown in FIG. 1, the radio network controller RNC integrally controls multiple radio base stations Node-B. Accordingly, there is a problem that the conventional mobile communication system has difficulty in performing a control for changing a transmission rate of a channel rapidly (for example, approximately 1 to 100 ms), due to processing load, processing delay, or the like.
In the conventional radio network controller RNC, there is also a problem that costs for implementing an apparatus and operating a network are substantially increased even if the control for changing a transmission rate of a channel rapidly can be performed.
Accordingly, in the conventional mobile communication system, a transmission rate of a channel is usually controlled and changed on the order of a few hundred milliseconds to a few seconds.
Consequently, in the conventional mobile communication system, when burst data transmissions are performed as shown in FIG. 2(a), the data are to be transmitted by allowing low speed, high delay, and low-transmission efficiency as shown in FIG. 2(b), or, as shown in FIG. 2(c), by reserving radio resources for high speed communications and by allowing the wasting of radio band resources in an unoccupied state and hardware resources in the radio base station Node-B.
Note that it is assumed that the radio resources in the vertical axis in FIG. 2 includes both of the above-described radio band resources and hardware resources.
Then, the “3GPP” and the “3GPP2”, which are international standardization groups of the third generation mobile communication system, have discussed a method for controlling high-speed radio resources of a layer 1, and a media access control (MAC) sub-layer (a second layer) between a radio base station Node-B and a mobile station UE, so as to utilize the radio resources effectively. Such discussions or discussed functions will be hereinafter collectively referred to as the “Enhanced Uplink (EUL)”.
The radio resource control methods that have heretofore been examined within the “Enhanced Uplink” are roughly classified into the following three categories. Hereinafter, an overview will be given of such radio resource control methods.
First, there has been examined a radio resource control method called “Time & Rate Control”.
In such a radio resource control method, a radio base station Node-B determines, at each predetermined timing, which mobile station UE to be allowed to transmit user data and the transmission rate of user data, and informs the mobile station UE of information related to the transmission rate of user data (or the maximum allowable transmission rate of user data) along with the mobile station ID.
Then, the mobile station UE specified by the radio base station Node-B transmits user data at the specified timing and the transmission rate (or within a range of the maximum allowable transmission rate).
Second, there has been examined a radio resource control method called “Rate Control per UE”.
In such a radio resource control method, whenever a mobile station has user data to be transmitted to a radio base station Node-B, the mobile station is allowed to transmit the user data. As to the maximum allowable transmission rate of the user data, however, the mobile station UE uses one which is determined by the radio base station Node-B for each transmission frame or each plurality of transmission frames, and which is then notified to the mobile station UE.
Here, when providing a notification of the maximum allowable transmission rate, the radio base station Node-B provides a notification of the maximum allowable transmission rate itself at the timing, or a relative value of the maximum allowable transmission rate (for example, a binary value of Up/Down).
Thirdly, there has been examined a radio resource control method called “Rate Control per Cell”.
In such a radio resource control method, a radio base station Node-B broadcasts a transmission rate of user data common to mobile stations UE in communications, or information required for calculating the transmission rate, and each of the mobile stations determines a transmission of user data based on the received information.
Ideally, the “Time & Rate Control” and the “Rate Control per UE” can be the best control methods for improving uplink radio capacity. However, since the radio base station Node-B is required to assign a transmission rate of user data by recognizing the amount of data accumulated in a buffer of the mobile station UE or a transmission power of the mobile station UE, or the like, in these methods, there is a problem that a control load on the radio base station Node-B increases.
In addition, these radio resource control methods have another problem that the overhead caused by exchanging control signals increases.
On the other hand, the “Rate Control per Cell” has an advantage that a control load by a radio base station Node-B is small, since the radio base station Node-B broadcasts information common to cells, and each mobile station UE autonomously finds a transmission rate of user data based on the received information.
However, since the radio base station Node-B needs to be configured to be capable of receiving uplink user data transmitted from any mobile station UE, there is a problem that the device scale of the radio base station Node-B has to increase in order to effectively utilize uplink radio capacity.
With this regard, a method (Autonomous ramping method), for example, is proposed as described in the Non-Patent Document 1. In this method, a mobile station UE increases, in accordance with a predetermined rule, a transmission rate of user data from an initial transmission rate provided in advance, and the radio station Node-B is accordingly prevented from excessively allocating a radio capacity. This also prevents an increase of the device scale of the radio base station Node-B.
In this method, a radio base station determines the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) based on hardware resources or radio resources (for example, the amount of interference in uplink) in each sector, and controls the user transmission rate of a mobile station in communications. Hereinafter, descriptions will be specifically given of a control method based on hardware resources and a control method based on the amount of interference in uplink.
In the control method based on hardware resources, the radio base station is configured to broadcast the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) to mobile stations connected to sectors under the radio base station.
In a case where hardware resources are about to run out because a transmission rate of user data in a mobile station connected to the sector under the radio base station increases, the radio base station sets the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) lower to prevent an occurrence of a lack of hardware resources.
On the other hand, in a case where there are some extra hardware resources because the transmission of user data by a mobile station connected to the sector under the radio base station ends or the like, the radio base station sets the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) higher again.
Furthermore, in the control method based on the amount of interference in uplink, a radio base station is configured to broadcast the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) to a mobile station connected to the sector under the radio base station.
In a case where the transmission rate of user data of the mobile station connected to the sector under the radio base station increases, and where the amount of interference in uplink (for example, a noise rise) exceeds the allowable value (for example, the maximum allowable noise rise), the radio base station sets the maximum allowable transmission rate lower, and keeps the amount of interference in uplink within the allowable value (refer to FIG. 3).
On the other hand, in a case where the amount of interference (for example, a noise rise) in uplink is kept within the allowable value (for example, the maximum allowable noise rise) with some margin because the transmission of user data of the mobile station connected to the sector under the radio base station ends or the like, the radio base station again sets the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) higher (refer to FIG. 3).
Note that in general, a serving cell, which performs a scheduling control in uplink of each of mobile stations, is configured to transmit an absolute rate grant channel (AGCH: Absolute Grant Channel) for notifying the maximum allowable transmission rate to each of the mobile stations, and a non-serving cell other than the serving cell is configured to transmit a relative rate grant channel (RGCH: Relative Grant Channel) for adjusting the maximum allowable transmission rate (or a parameter related to the maximum allowable transmission rate) to each of the mobile stations.
Here, specifically, in a case where the non-serving cell determines that the amount of interference from a different cell is large, the non-serving cell transmits a “Down” instruction in the relative rate grant channel (RGCH); otherwise, the non-serving cell transmits a “Don't care” instruction in the relative rate grant channel (RGCH).
Note that as shown in the Non-Patent Document 2, a serving cell is configured not to transmit a relative rate grant channel (RGCH) in the method (Autonomous ramping method) in which a mobile station is configured to automatically increase the transmission rate of user data up to the maximum allowable transmission rate.
In the conventional Autonomous ramping method, however, a user transmission rate in a mobile station temporarily decreases in a case where a “Down” instruction is transmitted from a non-serving cell to the mobile station, but increases immediately after the decrease of the user transmission rate. Accordingly, there is a problem that a relative rate grant channel (RGCH) transmitted from the non-serving cell does not effectively operate. This further produces another problem that a relative rate grant channel (RGCH) merely consumes the radio capacity in the downlink.    [Non-Patent Document 1] 3GPP TSG-RAN R1-040773    [Non-Patent Document 2] 3GPP TS25.309 v6.0.0 (RP-040486)